To compare hepatic and extrahepatic microsomal xenobiotic oxidative metabolism in several vertebrate and invertebrate marine species, to characterize the hepatic mixed-function oxidase system of the little skate, Raja erinacea, since it possesses relatively high enzyme activity, to investigate some xenobiotic conjugating enzymes in marine vertebrates and invertebrates, and to study the effects of environmental contaminant administration on in vitro xenobiotic mixed-function oxidation and conjugation by tissues from marine elasmobranchs and teleosts.